Version:            (using KDE KDE 3.5.6)
Installed from:    Ubuntu Packages
OS:                Linux

It is not clear what ordering simpleviewerexport is using to create the sequence in gallery.xml. 
My wish is it to be data-driven, or selectable, but it appeared to me to be filename-based. 
So I first aligned all the times in the EXIF *and* of the file with the tools in DigiKam. Checked with other applications and with the terminal. 
Then I changed the filename to reflect the time, e.g.: IA070126-222127_0001.JPG (my initials, date in ISO format, time and sequential number). 
I then tagged all the images I wanted to be exported to simpleviewer with a special tag ('simpleviewer') and then I exported the images by selecting 'tag:simpleviewer' (since you cannot export a selection of images, this is the quickest way I can see to do it).
The order is *almost* correct, but not correct at 100%. For example I got:

<NAME>IA070128-130827_0117.JPG</NAME>
<CAPTION>Ujjain, 60km from Indore</CAPTION>
</IMAGE>
<IMAGE>
<NAME>IA070128-135511_0121.JPG</NAME>
<CAPTION>Corn sellers</CAPTION>
</IMAGE>
<IMAGE>
<NAME>IA070127-103404_0019.JPG</NAME>
<CAPTION>In a temple in Indore</CAPTION>
</IMAGE>
<IMAGE>
<NAME>IA070127-103443_0022.JPG</NAME>
<CAPTION>View from a temple, Indore</CAPTION>
</IMAGE>


As you can see, the filename ordering is incorrect. I can also furnish the images if needed.